Gammaherpesviruses are closely associated with the development of lymphoproliferative disease and lymphomas, as well as other cancers. The long-term goal of this research is to understand how gammaherpesviruses manipulates normal B or T cell development to persist within the lymphoid compartment of the infected host. Understanding the mechanisms used by gammaherpesviruses to persist in the infected host may lead to the development of strategies for interfering with chronic infection. The focus of the proposed studies on murine gammaherpesvirus 68 (gammaHV68; also referred to as MHV-68) represents an ongoing effort to develop a tractable small animal model for characterizing establishment and maintenance of gammaherpesvirus infection. Aim 1. Analyze gammaHV68 latency in B cells in vivo. 1.a. Quantitate B cell and non-B cell latency in the spleen as a function of time after intraperitoneal and intranasal infection; and 1.b. Characterize the phenotype(s) of latently infected B cells; Aim 2. Quantitate turnover and dynamics of gammaHV68 latency in vivo; 2.a. Generate and characterize replication-deficient oHV68 mutants to determine the half-life of latency reservoirs in vivo; 2.b. Analyze spread of B cell latency by adoptive transfer of splenocytes from naive and latently infected immunocompetent mice into Rag 1-deficient mice; and 2.c. Monitor virus trafficking through B cells using genetically-marked viruses. Aim 3. Assess the requirement for B cell latency for long-term gammaHV68 infection. 3.a. Generate recombinant viruses harboring a conditionally expressed diphtheria toxin gene; 3.b. Analyze conditional diphtheria toxin expressing viruses in normal and tissue-specific Cre recombinase expressing mice; and 3.c. Generate and characterize mice that conditionally express cre recombinase activity - utilization with conditional diphtheria toxin expressing gammaHV68.